That followed falls of more than 1% in the UK and Europe, as skittish investors switched out of stocks into less risky assets.

Demand for bonds saw benchmark US 10-year bond yields fell by 8 basis points overnight to around 2.8%, while money also flowed into the safe-haven Japanese yen.

And a stronger currency was one factor which weighed on Japan's export-heavy Nikkei stock index when markets opened this morning.

Japanese stocks immediately slumped and a short time ago the Nikkei was down more than 4% — it's worst one-day fall since the market meltdown on February 6.

According to AxiTrader's Greg McKenna, the price action seen in global stocks over the last 24 hours is cause for some serious concern.

"Last night's last two hours of trade on the New York Stock Exchange was indicative of an evaporating bid. The market finished near the lows and we've seen an extension of that selling today," McKenna said.

"There's probably a rising chance that we see stock prices globally enter a bear market. That would mean a further 10% below the February lows."

"The reason is uncertainty. Just when traders were gearing up for an acceleration in the US economy — when it looked like the global economy might have one or two years of genuinely synchronized growth — we've had the spectre of inflation. Now Trump's tariffs and a trade war materially increase uncertainty."